POS0185 BELIMUMAB DISRUPTS MEMORY B-CELL TRAFFICKING IN PATIENTS WITH SYSTEMIC LUPUS ERYTHEMATOSUS
Authors: E. J. Arends, M. Zlei, C. M. Tipton, J. Cotic, Z. Osmani, F. de Bie, S. Kamerling, A. van Maurik, R. Dimelow, Y. I. Gregan, N. L. Fox, T. Rabelink, D. Roth, I. Sanz, J. J. M. van Dongen, C. van Kooten, Y. K. O. Teng
Journal: Annals of the Rheumatic Diseases (2022)

Background Belimumab (BEL), a recombinant human monoclonal antibody directed against B-cell activating factor (BAFF), is the first approved biological agent for patients with active systemic lupus erythematosus (SLE) and lupus nephritis (LN). 1 BEL inhibits primary humoral immune responses by depleting naïve B cells that are dependent on BAFF for their survival while secondary humoral immune responses by memory B cells (MBCs) remain intact. Indeed, some studies reported an increase of circulating MBCs following neutralisation of BAFF. 2-4 So far, these effects of BEL on the MBC compartment in SLE patients have not been investigated. Objectives This study aimed to establish the dynamics of circulating MBCs in patients with SLE treated with BEL and to perform an in-depth analysis of the impact of BEL on the MBC compartment. Methods First, a retrospective meta-analysis was performed by pooling individual patient MBC flow cytometry data from 1245 patients with SLE treated with BEL 10 mg/kg IV or placebo (PBO) from four randomised clinical trials ( NCT00071487 , NCT00410384 [BLISS-76], 3 NCT01632241 [EMBRACE], 5 NCT01649765 [PLUTO] 6 ). Second, extensive B-cell subset phenotyping was performed prospectively by employing high-sensitivity flow cytometry (HSFC) based on EuroFlow protocols 7 in patients with active SLE (from the BLISS-BELIEVE trial [ NCT03312907 ]) 8 and with severe SLE/LN (from the SynBioSe-2 trial [ NCT03747159 ]) 9 treated with BEL. Additionally, in-depth characterisation of surging MBCs in circulation was performed by single-cell RNA sequencing (scRNA-seq). Results By comparing BEL-treated with PBO-treated patients with SLE, a substantial increase in circulating MBC counts was established 4 weeks after BEL initiation, gradually returning to baseline by Week 52. The increase of MBCs was most prominent in BEL-treated patients with higher SLE disease activity (SLE Disease Activity Index &gt;9), serologically active patients (dsDNA positive and/or low complement levels) and with younger age (below 18 years). HSFC established that the increase was non-specific and observed in a broad range of MBC subclasses peaking as early as 2 weeks after BEL initiation. Subsequent scRNA-seq analysis of the emerging MBCs revealed a non-proliferating phenotype with a prominent decrease in activation status. In these circulating MBCs, a large amount of migration and adhesion genes were downregulated suggesting that the accumulation of MBCs following BEL treatment was related to their impaired cell-cell adhesion, disrupting cell-trafficking and preventing extravasation. Conclusion After initiation of BEL treatment, a substantial increase of circulating MBCs was firmly established and was most notable in patients with severe, serologically active SLE/LN. The surge of circulating MBCs appeared to be associated with disrupted lymphocyte trafficking of MBCs, thereby suggesting a new potential therapeutic mechanism of BEL on MBCs in SLE. These findings have important implications to our understanding and consequent improvement of B-cell targeted treatment strategies in patients with active SLE and LN, as MBC accumulation in circulation might allow for more efficient targeting of the B-cell compartment. References [1]GlaxoSmithKline. Benlysta US prescribing information. 2021 [2]Wallace DJ, et al. Arthritis Rheumatol 2009;61(9):1168–78 [3]Furie R et al. Arthritis Rheumatol 2011;63(12):3918–30 [4]Stohl W et al. Arthritis Rheumatol 2012;64(7):2328–37 [5]Ginzler E et al. Arthritis Rheumatol 2022;74(1):122–3 [6]Dimelow R et al. Clin Pharmacol Drug Dev 2021;10(6):622–33 [7]Blanco E et al. J Allergy Clin Immunol 2018;141(6):2208–19 [8]Teng YKO et al. BMJ Open 2019;9(3):e025687 [9]ClinicalTrials.gov NCT03747159 . Accessed January 19 2022 Acknowledgements This analysis of the GSK Study 205646 was funded by GlaxoSmithKline (GSK). Editorial support was provided by Nicholas Thomas, PhD, Fishawack Indicia Ltd. UK, part of Fishawack Health, and was funded by GSK. The EuroFlow-based HFSC was technically supported by Alita van der Sluijs and Sandra de Bruin and data acquisition was performed at the Flow cytometry Core Facility of Leiden University Medical Center, Leiden, NL. Disclosure of Interests Eline J. Arends: None declared, Mihaela Zlei Grant/research support from: GSK (flow cytometry studies for GSK BLISS-BELIEVE study NCT03312907 ), Christopher M. Tipton: None declared, Jasna Cotic Shareholder of: GSK, Employee of: GSK, Zgjim Osmani: None declared, Fenna de Bie Grant/research support from: GSK (flow cytometry studies for GSK BLISS-BELIEVE study NCT03312907 ), Sylvia Kamerling: None declared, Andre van Maurik Shareholder of: GSK, Employee of: GSK, Richard Dimelow Shareholder of: GSK, Employee of: GSK, Yun Irene Gregan Shareholder of: GSK, Employee of: GSK, Norma Lynn Fox Shareholder of: GSK, Employee of: GSK, Ton Rabelink: None declared, David Roth Shareholder of: GSK, Employee of: GSK, Ignacio Sanz Consultant of: Yes. GSK, BMS, Janssen, Kyverna, Jacques J.M. van Dongen Consultant of: BD Biosciences and Cytognos (fees for LUMC), Grant/research support from: GSK (flow cytometry studies for GSK BLISS-BELIEVE study NCT03312907 ), Cees van Kooten: None declared, Y.K. Onno Teng Consultant of: GSK, Aurinia Pharmaceuticals, Novartis, KezarBio, Grant/research support from: GSK